The proposed research is divided into three main sections: 1. Standardization of Techniques of Bioassay of Antibiotics in Ocular Tissues: Two approaches to bioassay of ocular tissues, namely homogenization of specimens with extraction of antibiotic in liquid vs. direct plating of trephined samples on seeded agar, will be compared to determine: (a) the relation between results achieved by the two methods; (b) the explanation for differences; and (c) the optimal technique. 2. Comparison of the Ocular Penetration of Antibiotics Applied Locally to the Eye by Various Techniques: The penetration in the rabbit of various compartments of the eye by penicillin G, oxacillin, carbenicillin, cephalothin, cephaloridine, gentamicin and vancomycin administered by four regional techniques will be compared, namely: (a) topical drops ("fortified" and "commercial" concentrations); (b) corneal bath; (c) subconjunctival injection; (d) retrobulbar injection. In addition, (b) and (d) will be done together with iontophoresis. Normal eyes will be studied as well as those with corneal ulcers due to lye or to Pseudomonas aeruginosa or induced bacterial endophthalmitis. 3. The effect of Soft Lenses on the Penetration of Antibiotic into the Cornea and Anterior Chamber: The effect of Soflens and Softcon soft contact lenses on the penetration of topically-applied gentamicin and oxacillin into the cornea and aqueous of rabbits with normal and ulcerated corneas will be examined. In addition, the uptake of several additional antibiotics by such lenses in vitro, as well as the facility with which drug may be eluted from them, will be measured. BIBLIOGRAPHIC REFERENCE: Barza, M., Baum, J.L. and Kane, A. Inhibition of antibiotic activity in vitro by synthetic melanin. Anti-microbial agents and chemotherapeutics. Antimicrobial Agents and Chemotherapy 10 (3): 569, 1976.